The present invention relates to an improvement of a copying machine, especially of a copying machine of a clamshell type.
In general, a copying machine of this type is composed of a clamshell structure wherein a main frame thereof can be opened with a conveyance path for a recording sheet as a boundary line, so that jam (clogging with paper) clearance may be carried out easily. To be concrete, the opening side of the main frame is arranged to be urged by an urging means such as a gas spring or the like so that it may be opened or closed around a supporting shaft provided on the sheet feeding side.
Not only the copying machine of the type mentioned above but also the latest copying machine are provided respectively with an ADF (automatic document feeder) unit that serves also as a document holder. When making copies from a book or a magazine, the ADF unit is opened and a document is placed on a platen glass, while when making copies from a sheet document, the ADF unit is closed for automatic feeding of documents.
However, when an ADF unit which serves also as a document holder is provided on the top of the main frame of the aforementioned conventional copying machine capable of being opened in a clamshell type, load imbalance is caused because of the supporting shaft side for opening and closing which is heavy, resulting in a fear that troubles such as fluttering opening and closing of a clamshell mechanism on the main frame might happen, which has been a problem.
Namely, in a conventional ADF unit, a supporting shaft for its opening and closing is located at its rear side for its easy opening and closing. However, a heavy portion such as a driving mechanism is provided in the vicinity of the supporting shaft for opening and closing. Therefore, on the opening and closing side of a copying machine on which an ADF unit is mounted, the rear portion is heavier than the front portion, resulting in a fear that a strain or a deformation is caused on the clamshell mechanism of the main frame and the opening and closing actions become unstable.
In view of the aforementioned point, the first object of the invention is to provide a copying machine equipped with a means capable of solving the load imbalance caused when an ADF unit is mounted on the copying machine.
Further, in a copying machine of this separated type wherein the copying machine is divided vertically into an upper half and a lower half, there is provided, between the upper half and the lower half, an elastic supporting member for supporting the upper half. When the elastic force of the supporting member is too small, the upper half can not be supported, while when it is too large, greater force is needed when the upper half is closed manually.
Incidentally, it is a recent trend that many functions are added to a copying machine, and it is considered that a copying machine of a separated type is equipped, as needed, with a mechanism called an automatic document feeder (ADF) capable of feeding automatically a document onto a document stand instead, for example, of feeding manually a plurality of documents one sheet by one sheet onto a document stand. In this case, due to tolerable weight of the ADF, total weight of the separated upper half equipped with the ADF is considerable. Therefore, the supporting force suitable for supporting the upper half without ADF is not sufficient for supporting the upper half with ADF. When designing from the beginning to give the supporting force sufficient for supporting the upper half with ADF, the supporting force is too great to pull down easily the upper half manually.
As a method for solving this problem, there are disclosed methods in Japanese Patent O.P.I. Publication Nos. 42769/1985 and 51349/1987 wherein a counter balance is provided for supporting the upper half and the supporting point for the counter balance is changed depending on the weight of the upper half, or the similar balancer spring is provided and its hooking position is changed to change the supporting force. Unlike the foregoing, it has been further suggested to change a gas spring to a stronger one.
However, the method to change the supporting position or the hooking position for the balancer spring when mounting or dismounting an ADF requires strong force for holding the balancer spring. Further, in the method wherein a balancer spring is replaced with the stronger one when mounting an ADF, one operator must replace a balancer spring while holding it with strong force when the other operator is keeping the upper half in an opened state, which means a tough and time-consuming work.
The present invention has been devised in view of the aforementioned point, and its second object is to provide a copying machine of a separated type wherein a work for coping with the change in weight of an upper half caused by mounting or dismounting of an optional device such as an ADF is easy.